This invention relates mainly to an actuator for operatively changing an auxiliary transmission for use in an automobile, a tractor etc, particularly to a diaphragm type vacuum actuator having two diaphragms and being actuated utilizing vacuum.
An object of this invention is to prevent abnormal deformation or breakage of a diaphragm as well as to prevent water and dust entering an intermediate chamber between two diaphragms from outside, thus permitting the diaphragms to function always in a good condition.
Another object of this invention is to securely prevent air leakage even when a rod becomes eccentric due to error of mounting when assembling it case, or when oscillating movement of the rod occurs.
In order to accomplish the above object, in this invention air passages are formed in piston plates, one end of each of the air passages is interconnected to the intermediate chamber, and the other end thereof is interconnected to the chambers under atmospheric pressure. A rod is movably provided in the case and has piston plates mounted thereon. The piston plates are connected to an inner peripheral surface of the case by two diaphragms so as to divide the inside of the case into a first chamber and a second chamber and to form an intermediate chamber in between both diaphragms. The rod is moved by subjecting one of said first and second chambers to vacuum and by opening the other thereof to atmospheric pressure.
Further, in order to accomplish the second object, a bearing support ring and a seal are fitted onto an outer peripheral surface of the rod, the seal being engaged with and held by the support ring. The seal is urged against a peripheral surface of a rod inserting hole of the case in the axial direction by means of suitable spring means. The seal and the support ring are made movable in the radial direction in conformity with a radial deviation of the rod.